1. Field of the Invention
The present invention relates to a switching power supply unit configured to produce switching output obtained by switching a DC input voltage at an output winding of a power conversion transformer.
2. Background Art
Generally, an electric vehicle is equipped with a low voltage battery (accessory battery) for outputting a low DC voltage such as about 14 V as a power supply for driving in-vehicle instruments (accessories) such as a wiper, a headlight, a room light, an audio instrument, an air conditioner, and various measuring instruments, and equipped with a high voltage battery (main battery) for outputting a high DC voltage such as about 350 to 500 V as a power supply for driving a motor. Typically, charge operation to such a low voltage battery is performed by rectifying an AC output voltage from an AC generator driven in terms of rotation of an engine to obtain a high DC voltage, and converting such a DC input voltage into a relatively low DC voltage using a switching power supply unit (DC/DC converter), and then supplying the low DC voltage to the low voltage battery. Charge operation to the high voltage battery is performed by supplying the DC input voltage from an engine to the high voltage battery. For example, as described in Japanese Unexamined Patent Publication No. 8-317508, the switching power supply unit performs voltage conversion by temporarily converting a DC input voltage into an AC voltage using an inverter circuit, then transforming the AC voltage using a voltage conversion transformer and reconverting the transformed AC voltage into a DC voltage using a rectifier circuit or the like.